This invention is generally related to a method and device for fabricating a magnetoelastic torque sensor. More particularly, this invention is related to a method and device for reducing magnetic hysteresis in a magnetoelastic torque sensor.
A magnetoelastic torque sensor utilizes the Inverse-Wiedmann Effect that generates a magnetic field in a magnetoelastic material responsive to the application of torque. A magnetoelastic torque sensor includes a substrate that bears an applied torque and that supports a band of magnetoelastic material. The magnetoelastic band is imparted with a circumferential stress that provides a magnetic easy axis that in turn provides a desired circumferential magnetic field within the magnetoelastic band. Torque on the substrate is transmitted to the band of magnetoelastic material to induce a distortion in the circumferential orientation of the magnetic field. The torque applied to the substrate causes the normally circumferentially orientated magnetic field to become distorted such that the magnetic field is helically shaped. The distortion away from the circumferential direction is measured by a magnetic field detection device. The magnitude and amplitude of the distortion corresponds to the torque applied to the substrate.
Disadvantageously, in some instances the magnetic field does not return to the desired circumferential orientation once torque is released. The remnant axial components of the magnetic field can cause a shift in the zero point known as hysteresis. At least a portion of the zero shift is caused by smaller than desired circumferential stress in the magnetoelastic band and a undesirably high magnetocrystalline anisotropy in the magnetoelastic material. Material properties of the magnetoelastic material are selected for compatibility with a specific application and in some instances materials may be selected and utilized that do not limit hysteresis.
Accordingly, it is desirable to develop a method and device that accommodates undesirable hysteresis effects in a magnetoelastic material and provides an economically favorable utilization of materials.